Spoilers for Dragon Ball Super Ahead!

Zamasu (ザマス Zamasu) refers to the true identity of several characters who serve as the main antagonists of the "Future" Trunks Saga of Dragon Ball Super

Originally, Zamasu was the former North Kai of Universe 10: The Macho Universe, serving as an apprentice under the current Supreme Kai, Gowasu to one day replace him. However, during his studies he became increasingly distrustful of mortals due to there use of wisdom and skill to perpetuate, violence, evil, and stupidity, thus defeating the purpose of creation. This dislike reached a zealous level of hatred when he met the stupidly powerful Son Goku who at that point wielded a power that greatly surpassed the majority of deities yet had no respect or reverence for them or the cosmic order of the multiverse at large. As well as hatred towards the other deities for their passiveness. This is what lead to Zamasu creating and enacting Project Zero Mortals to attempt to wipe out all mortal life and ascend to the throne as the one and only god of all creation.

Zamasu is a lean-built individual of fairly tall height. He has pale green skin, gray irises, white eyebrows, and white hair in the style of a mohawk. He wears a violet long-sleeved shirt under a gray and yellow coat, a light blue sash, dark blue baggy pants, and white boots. He also wore orange Potara-like earrings before stealing Gowasu's Green ones.

As Goku Black he has almost the exact same appearance of Son Goku except with narrower eyes, darker skin, sharper features, and a somewhat leaner build. In addition to wearing a black gi with white boots and a red sash.

Project Zero Mortals or the Zero Mortal Plan had 5 steps:

• Step 1. Kill Gowasu and Steal his Potara Earrings and Time Ring to become the Supreme Kai of Universe 10.
• Step 2. Switch bodies with (what Zamasu believed to be) the strongest being in existence with the Super Dragon Balls. This turned out to be Son Goku, whom he killed after switching bodies with him along with his family. This version of Zamasu would come to be known as Goku Black.
• Step 3. Use the Time Ring to travel to alternate timelines until a suitable one to rule is discovered. He ultimately settled on Future Trunks's Timeline due to the fact that the Supreme Kai and God of Destruction of Universe 7 had already died.
• Step 4. Team up with the Zamasu of that timeline and use the Super Dragon Balls to make him immortal. Also destroy the Super Dragon Balls so they cannot be used against them afterwards.
• Step 5. Kill everyone. Starting with the surviving Supreme Kais to ensure that the remaining Gods will not stop them and then all of mortal kind within the multiverse.

There are many different version of Zamasu:

• Present Zamasu - The Zamasu from the present timeline. He is destroyed by Beerus before he can begin Project Zero Mortals.
• Goku Black - The original Zamasu who first started Project Zero Mortals. Came to physically resemble Son Goku after switching bodies with him
• Future Zamasu - The Zamasu originating from Future Trunks's Timeline. Obtained immortality to serve as the Ultimate Shield to Goku Black's Ultimate Sword
• Fused Zamasu - Created via Potara Fusion between Future Zamasu and Goku Black. Has the height and build of Goku with the body and appearance of Zamasu. His hair is a chross between Zamsu's natural hair style and Goku's Super Saiyan Style. He wears version of Zamasu's Supreme Kai Uniform with Goku Black's Color Scheme
• Corrupted Zamsu - Due to the paradoxical nature of Future Zamasu's Immortality and Goku Black's lack there of, Fused Zamasu's regenerative abilities only worked halfway. The result is half of Zamasu's body becoming a large, grossly disproportionate, purple sludge as he tried to regenerate from severe damage and exploit Goku Black's Saiyan Power.
• Infinite Zamasu - Following the death of Fused Zamsu, Future Zamasu's immortality allowed him to fuse his spirit, now separated from any kind of physical form, with the rest of the Universe making him omnipresent and virtually invincible. He was erased from existence, along with the entire time line by Future Zeno.